The present invention relates to an endoluminal vascular prosthesis, and in particular, to a self-expanding bifurcated prosthesis for use in the treatment of abdominal aortic aneurysms.
An abdominal aortic aneurysm is a sac caused by an abnormal dilation of the wall of the aorta, a major artery of the body, as it passes through the abdomen. The abdomen is that portion of the body which lies between the thorax and the pelvis. It contains a cavity, known as the abdominal cavity, separated by the diaphragm from the thoracic cavity and lined with a serous membrane, the peritoneum. The aorta is the main trunk, or artery, from which the systemic arterial system proceeds. It arises from the left ventricle of the heart, passes upward, bends over and passes down through the thorax and through the abdomen to about the level of the fourth lumbar vertebra, where it divides into the two common iliac arteries.
The aneurysm usually arises in the infrarenal portion of the diseased aorta, for example, below the kidneys. When left untreated, the aneurysm may eventually cause rupture of the sac with ensuing fatal hemorrhaging in a very short time. High mortality associated with the rupture led initially to transabdominal surgical repair of abdominal aortic aneurysms. Surgery involving the abdominal wall, however, is a major undertaking with associated high risks. There is considerable mortality and morbidity associated with this magnitude of surgical intervention, which in essence involves replacing the diseased and aneurysmal segment of blood vessel with a prosthetic device which typically is a synthetic tube, or graft, usually fabricated of Polyester, Urethane, DACRON(copyright), TEFLON(copyright), or other suitable material.
To perform the surgical procedure requires exposure of the aorta through an abdominal incision which can extend from the rib cage to the pubis. The aorta must be closed both above and below the aneurysm, so that the aneurysm can then be opened and the thrombus, or blood clot, and arteriosclerotic debris removed. Small arterial branches from the back wall of the aorta are tied off. The DACRON(copyright) tube, or graft, of approximately the same size of the normal aorta is sutured in place, thereby replacing the aneurysm. Blood flow is then reestablished through the graft. It is necessary to move the intestines in order to get to the back wall of the abdomen prior to clamping off the aorta.
If the surgery is performed prior to rupturing of the abdominal aortic aneurysm, the survival rate of treated patients is markedly higher than if the surgery is performed after the aneurysm ruptures, although the mortality rate is still quite high. If the surgery is performed prior to the aneurysm rupturing, the mortality rate is typically slightly less than 10%. Conventional surgery performed after the rupture of the aneurysm is significantly higher, one study reporting a mortality rate of 66.5%. Although abdominal aortic aneurysms can be detected from routine examinations, the patient does not experience any pain from the condition. Thus, if the patient is not receiving routine examinations, it is possible that the aneurysm will progress to the rupture stage, wherein the mortality rates are significantly higher.
Disadvantages associated with the conventional, prior art surgery, in addition to the high mortality rate include the extended recovery period associated with such surgery; difficulties in suturing the graft, or tube, to the aorta; the loss of the existing aorta wall and thrombosis to support and reinforce the graft; the unsuitability of the surgery for many patients having abdominal aortic aneurysms; and the problems associated with performing the surgery on an emergency basis after the aneurysm has ruptured. A patient can expect to spend from one to two weeks in the hospital after the surgery, a major portion of which is spent in the intensive care unit, and a convalescence period at home from two to three months, particularly if the patient has other illnesses such as heart, lung, liver, and/or kidney disease, in which case the hospital stay is also lengthened. The graft must be secured, or sutured, to the remaining portion of the aorta, which may be difficult to perform because of the thrombosis present on the remaining portion of the aorta. Moreover, the remaining portion of the aorta wall is frequently friable, or easily crumbled.
Since many patients having abdominal aortic aneurysms have other chronic illnesses, such as heart, lung, liver, and/or kidney disease, coupled with the fact that many of these patients are older, the average age being approximately 67 years old, these patients are not ideal candidates for such major surgery.
More recently, a significantly less invasive clinical approach to aneurysm repair, known as endovascular grafting, has been developed. Parodi, et al. provide one of the first clinical descriptions of this therapy. Parodi, J. C., et al., xe2x80x9cTransfemoral Intraluminal Graft Implantation for Abdominal Aortic Aneurysms,xe2x80x9d 5 Annals of Vascular Surgery 491 (1991). Endovascular grafting involves the transluminal placement of a prosthetic arterial graft within the lumen of the artery.
In general, transluminally implantable prostheses adapted for use in the abdominal aorta comprise a tubular wire cage surrounded by a tubular PTFE or Dacron sleeve. Both balloon expandable and self expandable support structures have been proposed. Endovascular grafts adapted to treat both straight segment and bifurcation aneurysms have also been proposed.
Notwithstanding the foregoing, there remains a need for a structurally simple, easily deployable transluminally implantable endovascular prosthesis, with a support structure adaptable to span either a straight or bifurcated aortic aneurysm. Preferably, the tubular prosthesis can be self expanded at the site to treat the abdominal aortic aneurysm, and exhibits flexibility to accommodate nonlinear anatomies and normal anatomical movement.
There is provided in accordance with one aspect of the present invention, an endoluminal prosthesis having an endoskeleton for supporting tubular polymeric sleeve, and a partial exoskeleton for positioning at the anatomically proximal end, to minimize migration and risks of endoleaks. The prosthesis comprises at least one elongate flexible wire, formed into a plurality of axially adjacent tubular segments spaced along an axis. Each tubular segment comprises a zig-zag section of wire, having a plurality of proximal bends and distal bends. At least one of the plurality of proximal bends and plurality of distal bends have loops thereon. A tubular polymeric sleeve is carried by the prosthesis.
The prosthesis is radially compressible into a first, reduced cross sectional configuration for implantation into a body lumen, and self expandable to a second, enlarged cross sectional configuration at a treatment site in a body lumen. At least a first portion of wire in one tubular segment is positioned on a radially outwardly facing surface of the sleeve. A radially inwardly facing surface of the sleeve is in contact with a second portion of wire.
In one application, the prosthesis comprises at least six proximal bends on a distal segment, and at least three of the proximal bends reside on the outside of the tubular sleeve and the remainder of the proximal bends are positioned on the inside of the tubular sleeve. At least about 30%, and generally from about 40% to about 70% of the proximal bends on a distal segment reside on the outside of the tubular sleeve. In this context, distal refers to catheter distal which is the same as anatomically proximal. The proximal bends on the inside of the tubular sleeve are connected to distal bends on a proximally adjacent segment inside of the tubular sleeve.
In accordance with another aspect of the present invention, there is provided a tubular wire support for a bifurcated endoluminal prosthesis. The wire support comprises a main body support structure having a proximal end, a distal end and a central lumen extending along a longitudinal axis therethrough. A first branch support structure, having a proximal end, a distal end and a central lumen therethrough, is provided such that the distal end of the first branch structure is connected to the proximal end of the main body support structure. A second branch support structure, having a proximal end, a distal end and a central lumen extending therethrough is provided, such that the distal end of the second branch support structure is connected to the proximal end of the main body support structure. A plurality of radially outwardly extending barbs or treads are provided on the main body, integrally formed on the wire support. The main body support structure and first and second branch support structures are preferably self expandable from a radially collapsed state to a radially expanded state.
The wire in each support structure is formed into a plurality of segments, each segment comprising a series of proximal bends, a series of distal bends, and a series of struts connecting the proximal and distal bends. The barbs may be formed by bending at least one of the proximal or distal bends such that it inclines radially outwardly from the longitudinal axis of the corresponding support structure. Preferably, the anchors comprise a plurality of distal bends on the main body support structure, to provide anchoring at the anatomically proximal end of the implanted tubular wire support.
In accordance with further aspect of the present invention, there is provided a tubular wire support for combination with a sheath to produce a flexible bifurcated endoluminal prosthesis. The wire support comprises a main body support structure having a proximal end, a distal end and a central lumen extending therethrough, the support structure comprising at least a first and second axially adjacent tubular segments. Each segment comprises a plurality of wall struts connected by proximal and distal bends.
A first branch support structure, having a proximal end, a distal end and a central lumen therethrough is connected to the main body support structure. A second branch support structure, having a proximal end, a distal end and a central lumen extending therethrough, is connected to the main body support structure. At least two sliding links are provided in between the first and second segments on the main body support structure and at least one lock is provided on a wall strut for limiting axial movement of a sliding link along that strut.
In one application, the lock comprises a loop formed into the strut, for limiting the effective length of travel of the sliding link along that strut. At least about 30%, and in some devices at least 50%, and in other devices 100% of the links in between the first and second segments are provided with a sliding link configuration. At least about 30%, and in some applications at least about 50% of the sliding links are provided with a lock on the corresponding strut.
In accordance with a further aspect of the present invention, there is provided a flexible self expandable graft. The graft comprises a tubular main body support structure, having a proximal end and a distal end. The tubular body comprises at least a first tubular segment attached to a second tubular segment. A tubular polymeric sleeve surrounds at least a portion of the graft. Each of the first and second tubular segments comprise a plurality of proximal bends and distal bends connected by struts, surrounding a longitudinal axis such that a first strut is on a first side of the axis and a second strut is on a second side of the axis opposing the first side. In at least one segment, the first strut is shorter than the second strut. In some applications, at least two or three or four or more adjacent segments are provided with a shorter strut or struts on a first side of the axis compared to the corresponding strut or struts on the second side of the axis, to facilitate curvature of the graft.